In general, a conventional door-opening/closing device operated electrically does not respond if a pedestrian approaches the device too slowly. If a pedestrian stops walking, the device closes the door even if the pedestrian is in the area within which the device senses the presence of a human (hereinafter “device's detection area”). Also, if there is a power outage, the door that the device is to operate, together with the device's drive unit, needs to be moved by human power so as to open or close the door, which requires a large amount of human force. In order to prevent such operational failure and the resulting need for human force to be applied, a conventional device requires not only a source of primary electricity but also a source of backup electricity. In addition, a conventional device has many disadvantages, such as the adverse effects on human bodies and on precision equipment near the device of the electromagnetic waves used for the device's sensor.
In order to eliminate the above-mentioned disadvantages, many door-opening/closing devices that do not use electricity but use the potential energy obtained by the downward movement of a step plate stepped on by a pedestrian have been invented. In many of these devices, a door opening/closing mechanism is disposed on the floor, as well as in a door pocket and/or a transom, and therefore such a device requires a large space.
One example of the prior art is the door-opening/closing device described in Patent Document 1 (see FIG. 8). This door-opening/closing device has a mechanism such that a portion—specifically the portion that is immediately beneath a door—of a step plate is raised, and such that the front and rear ends—as seen by an pedestrian—of the step plate are affixed to the floor by hinges. The force by which the step plate is restored to its original raised position after having been stepped on is interlocked with a door-closing force. But this has the disadvantage of requiring a large space in the door's transom. Another disadvantage is that the acting force obtained from the stepping force varies depending on the specific position stepped on by a pedestrian.
The door-opening/closing device described in Patent Document 2 (see FIG. 9) has no mechanism in the door's transom, but it has a large mechanism in the door pocket. This large space needs to be taken into consideration when designing a building.